l6o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



probably the ancestor of Ca^ssidulus. It differs from Nuclcopygus in 

 having much more pronounced bourrelets, more widened phyllodes, 

 larger adoral tubercles, and a wider naked zone in interambulacrum 5. 



Remarks. — Mortensen was not aware that the apical system in 

 Rhynchopygus marmini was tetrabasal and considered Rhynchopygus 

 as a synonym of Cassidulus. I have also found a tetrabasal apical 

 system in Rhynchopygus macari (Smiser) and in Rhynchopygus 

 lapiscancri (Leske). These three species have many features in com- 

 mon and appear to be clearly congeneric, and distinct from Cassidulus. 

 They are small forms with supramarginal periprocts (the fact that 

 the periproct is transverse in R. marmini and R. macari and longi- 

 tudinal in R. lapiscancri does not seem to be of generic significance), 

 similar petals, and flat adoral surfaces. Their close relationship is 

 shown strikingly by their identical floscelles with extremely well- 

 developed bourrelets and broad, similar phyllodes. 



Rhynchopygus liisitaniciis (De Loriol) from the lowest Turonian 

 is the oldest species of this genus that I have studied. Its apical sys- 

 tem (text fig. 133) is tetrabasal not monobasal as previously thought. 

 Its phyllodes (text fig. 132) have more pores than found in the 

 Senonian species of this genus, confirming the suggestion made herein 

 that the number of phyllodal pores is reduced in many genera in 

 time. 



Kew (1920, pp. 138-142) placed all the American west coast spe- 

 cies of cassidulids in Rhynchopygus, which he considered to be a 

 subgenus of Cassidulus. I have studied the type specimens of these 

 species and do not believe that any of them belong in Rhynchopygus. 

 They all have monobasal apical systems ; three of them, C. ellipticus 

 Kew, C. calif ornicus Anderson, and C. ynesensis, are herein referred 

 to Cassidulus and C. mexicanus Kew to Rhyncholampas. 



Range and distribution. — Upper Cretaceous (Turonian-Maestrich- 

 tian) of Belgium, Holland, and France. The distribution of this 

 genus will not be known until all the species previously referred to 

 Cassidulus have been reexamined and their apical systems studied. 



DESCRIPTION OF TYPE SPECIES 



RHYNCHOPYGUS MARMINI (L. Agassiz) 



Plate 24, figures 1-4; text figures 134, 137 



Cassidulus marmini L. Agassiz, in L. Agassiz and Desor, 1847. Ann. Sci. Nat., 

 ser. 3, vol. 7, p. 157. 



Material. — Twelve specimens studied in the U. S. National Mu- 

 seum, and several in the Lambert Collection at the Sorbonne, Paris. 



